Semiconductor wafers are the substrates for current integrated circuits. The conventional production and performance of integrated circuits fabricated on a wafer are dependent on the choice, quality and dimensions of the semiconductor material of the wafer. Originally made of pure silicon, wafer compositions have evolved owing to the advent of new technologies. Thus, one example of how semiconductor wafers have evolved is the production of single-crystal SOI (Silicon On Insulator) wafers. In these wafers, the silicon layer useful for integration of devices is much thinner than hitherto, being of the order of a few tens of nanometers. A subjacent dielectric layer, interposed between the useful silicon layer and the silicon substrate, makes it possible not only to give the assembly rigidity but also to act as an electrical insulator. Thus, the performance of transistors produced in this type of wafer can be enhanced.
In some conventional semiconductor wafers, silicon is replaced with a semiconductor material having a lower electrical resistivity. An example of such a material is germanium. Thus, a silicon-germanium alloy on insulator wafers and a strained silicon-germanium alloy on insulator wafers have been proposed. The latter have an even lower resistivity due to the stresses exerted on the semiconductor layer. Germanium on insulator wafers has been made possible with processes similar to those already used to produce silicon on insulator wafers and described in, for example, the document “Réalisation en première mondiale du substrats Germanium sur Isolant (GeOI) [First production in the world of germanium-on-insulator (GeOI) substrates”] accessible on the Commissariat à l'Energie Atomique Internet site: www.cea.fr. This process essentially produces a weakened zone within the depth of a bulk material by using implanted ions to cause a fracture along the weakened plane and create a thin wafer. This process, however, produces only entire germanium-on-insulator wafers.
Germanium is a costly material and is less abundant than silicon. Moreover, the most effective technology uses silicon or germanium depending on the type of device (n-channel or p-channel transistor) or the type of function (electronic or optoelectronic). Thus, to combine the advantages of the two technologies, it may be advantageous to integrate the silicon and germanium technologies on the same integrated circuit. This is generally referred to as “co-integration”. Co-integration may thus require germanium-on-insulator zones to be locally integrated on a silicon substrate. The process described above therefore cannot be adapted to cases in which silicon and germanium technologies must be used together in integrated circuits.
There is therefore a need for a process to produce a layer of single-crystal first material on a second material, where the second material is located between at least two surface portions of a single crystal third material.